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12th Grade > Mathematics

STRAIGHT LINES MCQs

Straight Lines

Total Questions : 60 | Page 2 of 6 pages
Question 11. Without changing the direction of coordinate axes, origin is transferred to (h, k), so that the linear (one degree)
terms in the equation x2+y24x+6y7=0 are eliminated. Then the point (h, k) is
  1.    (3, 2)
  2.    (- 3, 2)
  3.    (2, - 3)
  4.    (1.7)
 Discuss Question
Answer: Option C. -> (2, - 3)
:
C
Putting x = x' + h, y = y' + k, the given equation transforms to
x2+y2+x(2h4)+y(2k+6)+h2+k27=0
To eliminate linear terms, we should have
2h - 4 = 0, 2k + 6 = 0 h = 2, k = -3
i.e., (h, k) = (2, -3).
Question 12. The equation of the internal bisector of BAC of ΔABC with vertices A(5, 2), B(2, 3) and C(6, 5), is
  1.    2x + y + 12 = 0
  2.    x + 2y – 12 = 0
  3.    2x + y – 12 = 0
  4.    x + 2y +12 = 0
 Discuss Question
Answer: Option C. -> 2x + y – 12 = 0
:
C
Let AD be the internal bisector of angle BAC cutting BC at D.
Now,AB=(52)2+(23)2=10andAC=(56)2+(25)2=10
since AD is the internal bisector of angle BAC,
BDDC=ABAC=1010=11
Coordinates of D are (2+62,3+52) i.e. (4, 4)
So, the equation of AD is
y2=2454 (x – 5) or 2x + y – 12 = 0
The Equation Of The Internal Bisector Of ∠BAC Of ΔABC Wit...
Question 13. If the orthocenter and circumcentre of a triangle are (0,0) and (3,6) respectively then the centroid of the triangle is
  1.    (1,2)
  2.    (2,4)
  3.    (23,43) 
  4.    (13,23) 
 Discuss Question
Answer: Option B. -> (2,4)
:
B
In any triangle centroid divides the line joining orthocenter and circumcentre internally in the ratio 2 : 1.
Applying section formula to find the point which divides the line joining (0,0) in the ratio 2:1 , we get the coordinated of centroid equal to (2,4).
Question 14. If the lines (pq)x2+2(p+q)xy+(qp)y2=0 are mutually perpendicular, then 
  1.     p = q
  2.    q = 0
  3.    p = 0
  4.     p and q may have any value 
 Discuss Question
Answer: Option D. ->  p and q may have any value 
:
D
Pair of straight lines represented by a second degree equation with coefficient of x2 as a and coefficient of y2 as bare perpendicular if a+b = 0. Herere a + b = 0 for every p and q.
Question 15. The equation of the internal bisector of BAC of ΔABC with vertices A(5, 2), B(2, 3) and C(6, 5), is
  1.    2x + y + 12 = 0
  2.    x + 2y – 12 = 0
  3.    2x + y – 12 = 0
  4.    x + 2y +12 = 0
 Discuss Question
Answer: Option C. -> 2x + y – 12 = 0
:
C
Let AD be the internal bisector of angle BAC cutting BC at D.
Now,AB=(52)2+(23)2=10andAC=(56)2+(25)2=10
since AD is the internal bisector of angle BAC,
BDDC=ABAC=1010=11
Coordinates of D are (2+62,3+52) i.e. (4, 4)
So, the equation of AD is
y2=2454 (x – 5) or 2x + y – 12 = 0
The Equation Of The Internal Bisector Of ∠BAC Of ΔABC Wit...
Question 16. The orthocenter of the triangle formed by the lines x + y = 1, 2x + 3y = 6 and 4x - y + 4 = 0 lies in
  1.    I quadrant
  2.    II quadrant
  3.    III quadrant
  4.    IV quadrant
 Discuss Question
Answer: Option A. -> I quadrant
:
A
Coordinates of A and B are (-3, 4) and (35,85)​ if orthocenter P(h, k)
The orthocenter Of The Triangle Formed By The Lines X + Y =...
Then, (slope of PA)× (slope of BC) = - 1
k4h+3×4=1
4k - 16 = -h - 3
h + 4k = 13....(i)
and slope of PB× slope of AC = - 1
k85h+35×23=1
5k85h+3×23=1
10k - 16 = 15th + 9
15th - 10k + 25 = 10
3h - 2k + 5 = 0 ...(ii)
Solving Eqs. (i) and (ii), we get h=37,k=227
Hence, orthocentre lies in I quadrant.
Question 17. Two points A and B have coordinates (1, 0) and (-1, 0) respectively and Q is a point which satisfies the relation
AQ - BQ = ± 1. The locus of Q is
  1.    12x2+4y2=3
  2.    12x2−4y2=3
  3.    12x2−4y2+3 = 0
  4.    12x2+4y2+3 = 0
 Discuss Question
Answer: Option B. -> 12x2−4y2=3
:
B
According to the given condition
(x1)2+y2(x+1)2+y2 = ±1
On squaring both sides, we get
2x2+2y2+1=2(x1)2+y2(x+1)2+y2
Again on squaring, we get 12x24y2=3.
Question 18. If h denote the A.M, k denote G.M of the intercepts made on axes by the lines passing through (1, 1) then (h, k) lies on
  1.    y2=2x
  2.    y2=4x
  3.    y=2x
  4.    x+y=2xy
 Discuss Question
Answer: Option A. -> y2=2x
:
A
a = x - intercept, b =y - intercept
2h=a+b,k2=ab
xa+yb=1​, substitute (1, 1)
1a+1b=1
a + b = ab
2h=k2y2=2x
Question 19. If A(4, -3), B(3, -2) and C(2, 8) are the vertices of a triangle, then its centroid will be 
  1.    (-3,3)
  2.    (3,3)
  3.    (3,1)
  4.    (1,3)
 Discuss Question
Answer: Option C. -> (3,1)
:
C
Let the centroid of the triangle be (x, y).
The centroid of a triangle is given by (x1+x2+x33,y1+y2+y33)
x=4+3+23=3
y=32+83=1
Question 20. A line through the point A(2, 0), which makes an angle of 30 with the positive direction of x-axis is rotated about A in clockwise direction through an angle 15. The equation of the straight line in the new position is
  1.    (2−√3)x−y−4+2√3=0
  2.    (2−√3)x+y−4+2√3=0
  3.    (2−√3)x−y+4+2√3=0
  4.    (2−√3)x−9y+4+2√3=0
 Discuss Question
Answer: Option A. -> (2−√3)x−y−4+2√3=0
:
A
Let AB be the initial position of the line and AC be its new position.
Slope of the line
AC=tan15=(23)
Equation of the line AC is
(y0)=(23)(x2)ory=(23)x4+23or(23)xy4+23=0
A Line Through The Point A(2, 0), Which Makes An Angle Of 30...

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