The value of n for which the expression 9x4−12x3+nx2−8x+4 becomes a perfect square is
A
12
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B
16
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C
18
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D
24
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Solution
The correct option is B16 Let the equation be of the form (ax2+bx+c)2=a2x4+b2x2+c2+2abx3+2bxc+2acx2 a2x4+2abx3+(b2+2ac)x2+c2+2bxc = 9x4−12x3+nx2−8x+4 Comparing the coefficients, a=3,c=2 2ab=−12 b=−2 Therefore, n=b2+2ac=4+12=16