Circles

Question
The slope m of a tangent through the point (7, 1) to the circle x2+y2=25 satisfies the equation
Options:
A. 12m2 + 7m - 12 = 0
B. 12m2 + 7m + 9 = 0
C. 12m2 - 7m - 12 = 0
D. 9m2 + 12m + 16 = 0

 Next Question
Answer: Option C
: C

Equation of a tangent to x2+y2 = 25 is y = mx ± 51+m2
This passes through (7, 1) 1 = 7m ± 51+m2
(17m)2=25(1+m2) 49m214m+1=25+25m2 24m214m14=0
12m2 - 7m - 12 = 0

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