Final Answer
$x^2-3x-4$
Step-by-step solution
Problem to solve:
$\left(x+1\right)\left(x-4\right)$
Solving method
1
We can multiply the polynomials $\left(x+1\right)\left(x-4\right)$ by using the FOIL method. The acronym F O I L stands for multiplying the terms in each bracket in the following order: First by First ($F\times F$), Outer by Outer ($O\times O$), Inner by Inner ($I\times I$), Last by Last ($L\times L$):
- ($F\times F$) is $(x)(x)$
- ($O\times O$) is $(x)(-4)$
- ($I\times I$) is $(1)(x)$
- ($L\times L$) is $(1)(-4)$
Then, combine the four terms in a sum: $(F\times F) + (O\times O) + (I\times I) + (L\times L)$:
$x\cdot x-4x+1x+1\cdot -4$
2
Multiply $1$ times $-4$
$x\cdot x-4x+1x-4$
3
Any expression multiplied by $1$ is equal to itself
$x\cdot x-4x+x-4$
4
When multiplying two powers that have the same base ($x$), you can add the exponents
$x^2-4x+x-4$
5
Combining like terms $-4x$ and $x$
$x^2-3x-4$
Final Answer
$x^2-3x-4$