Find the value of m:
A. 7
B. 21
C. 15 or 14
D. none of these
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given first eq is ,
x^2 + 10 x + 21 = 0
x^2 + 7 x + 3x + 21 = 0
x ( x + 7 ) + 3 ( x + 7 ) = 0
( x + 7 ) ( x + 3 ) = 0
x + 7 = 0 or x + 3 = 0
x = - 7 or x = - 3
putting these values one by one in second eq .
x^2 + 9 x + m = 0
(-7)^2 + 9 (-7) + m = 0
49 -63 + m = 0
m = 14
also
x^2 + 9 x + m = 0
(-3)^2 + 9 (-3) + m = 0
9 -27 + m = 0
m = 18
therefore m = 14 ---- from options
x^2 + 10 x + 21 = 0
x^2 + 7 x + 3x + 21 = 0
x ( x + 7 ) + 3 ( x + 7 ) = 0
( x + 7 ) ( x + 3 ) = 0
x + 7 = 0 or x + 3 = 0
x = - 7 or x = - 3
putting these values one by one in second eq .
x^2 + 9 x + m = 0
(-7)^2 + 9 (-7) + m = 0
49 -63 + m = 0
m = 14
also
x^2 + 9 x + m = 0
(-3)^2 + 9 (-3) + m = 0
9 -27 + m = 0
m = 18
therefore m = 14 ---- from options
pravinsir:
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