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2. Polynomials
easy
જો $49 x^{2}-b=\left(7 x+\frac{1}{2}\right)\left(7 x-\frac{1}{2}\right),$ હોય, તો $b$ ની કિંમત ............ છે.
A
$\frac{1}{4}$
B
$0$
C
$\frac{1}{\sqrt{2}}$
D
$\frac{1}{2}$
Solution
$49 x^{2}-b=\left(7 x+\frac{1}{2}\right)\left(7 x-\frac{1}{2}\right)$
$\Rightarrow \quad 49 x^{2}-b=(7 x)^{2}-\left(\frac{1}{2}\right)^{2}$
$=49^{2}-\frac{1}{4} \quad\left[\because(a+b)(a-b)=a^{2}-b^{2}\right]$
So, we get $b=\frac{1}{4}$
Hence, $(a)$ is the correct answer.
Std 9
Mathematics
