### Home > PC3 > Chapter 13 > Lesson 13.2.2 > Problem13-78

13-78.

Expand and simplify:

1. $\left(a+b\right)^4-\left(a-b\right)^4$

Use Pascal's triangle.

$\left(a^4+4a^3b+6a^2b^2+4ab^3+b^4\right)-\left(a^4+4a^3\left(-b\right)+6a^2\left(-b\right)^2+4a\left(-b\right)^3+\left(-b\right)^4\right)$

2. $\left(\sin\left(x\right)+\cos\left(x\right)\right)^4-\left(\sin\left(x\right)-\cos\left(x\right)\right)^4$

Use your answer from part (a) where $a=\sin\left(x\right)$ and $b=\cos\left(x\right)$.