Question

Mutiple by using appropriate indentity: ( 3x + 1 ) ( 3x – 8 )​

Answer 1

3x+1/3x=8

Cubing both sides

(3x+1/3x)^3=(8)^3

27x3+1/27x3+3(3x)(1/3x)(3x+1/3x)=512    ...(using the identity:(a+b)^3)

27x3+1/27x3+3(8)=512                           ...(3x*1/3x=1, 3x+1/3x=8)

27x3+1/27x3+24=512

27x3+1/27x3=512-24

27x3+1/27x3=488

PLS MARK ME AS BRAINIEST

Answer 2

$\Huge\mathfrak\color{red}{answer:}$

$\bf{Identity~to~be~used:}$

$\tt{~~~~~~~~(x+a)(x+b)=x^{2}+(a+b)x+ab}$

$\tt{: \longrightarrow (3x)^{2}+[1+(-8)~]3x+(1×-8)}$

$\tt{: \longrightarrow 9x^{2}+(-7)3x+(-8)}$

$\tt{: \longrightarrow {\color{red}{\bf 9x^{2}-21x-8}}}$