Multiply mentally
-$\left(3 x^{2}-\frac{10}{7}\right)\left(3 x^{2}+\frac{10}{7}\right)$
A) $9 x^{2}+140 x-\frac{100}{49}$
B) $9 x^{2}-\frac{100}{49}$
C) $9 x^{2}-140 x-\frac{100}{49}$
D) $9 x^{4}-\frac{100}{49}$

Question

Quizplus · Accepted Answer

This is an application of the difference of squares formula, $a^2 - b^2 = (a - b)(a + b)$, where $a = 3x^2$ and $b = \frac{10}{7}$. The result is $9x^4 - \frac{100}{49}$.

Multiply Mentally - (3x2−107)(3x2+107)\left(3 x^{2}-\frac{10}{7}\right)\left(3 x^{2}+\frac{10}{7}\right)(3x2−710​)(3x2+710​) A) 9x2+140x−100499 x^{2}+140 x-\frac{100}{49}9x2+140x−49100​ B) 9x2−100499 x^{2}-\frac{100}{49}9x2−49100​

Multiply Mentally
- $\left(3 x^{2}-\frac{10}{7}\right)\left(3 x^{2}+\frac{10}{7}\right)$ A) $9 x^{2}+140 x-\frac{100}{49}$ B) $9 x^{2}-\frac{100}{49}$