Question

What is the product (9t-4)(-9t -4)

Answer 1

Combine like terms: -81t^2 + 16

Answer 2

Hey Tro2, 

Lets find the product of your equation together, 

The question we are encountering is : What is the product (9t-4)(-9t-4)? 

          Lets simplify this step by step, shall we. 

$\left(9t-4\right)\left(-9t-4\right)$   : Equation 

           $\mathrm{Distribute\:parentheses\:using}:\quad \left(a+b\right)\left(c+d\right)=ac+ad+bc+bd$. 

Where : $a=9t,\:b=-4,\:c=-9t,\:d=-4$ .

This leads to $9t\left(-9t\right)+9t\left(-4\right)-4\left(-9t\right)-4\left(-4\right)$. 

Now we have to $\mathrm{Apply\:minus-plus\:rules}$. 

Where: $-\left(-a\right)=a,\:\:\:\:+\left(-a\right)=-a$ 

$-9t\cdot \:9t-9t\cdot \:4+4\cdot \:9t+4\cdot \:4$ 

$=-81t^2+16$