SOLUTION: how do I solve k^2-4k-5=0

Question 838873: how do I solve k^2-4k-5=0
Answer by mxgirl22(39) (Show Source): You can put this solution on YOUR website!
how do I solve k^2-4k-5=0

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1.) You can either factor or use the quadratic formula.

For this step I'll show you factoring since this is a nice trinomial.

k^2-4k-5=0

We need to find two numbers that will give us -5 when multiplied together and -4 when added together.

I like to set it up like this when I'm solving...

[_]+[_]=-4
[_]x[_]=-5

I know the only way to get -5 when multiplying is by having 1 & -5(or -1 and 5) but looking at what it needs to add up to it has to be 1 and -5.

[1]+[-5]=-4
[1]x[-5]=-5

Now use those numbers to factor.

k^2-4k-5=0

k^2+1k-5k-5=0

(k^2+1k)+(-5k-5)=0

k(k+1)-5(k+1)=0

k-5=0___&___k+1=0

k-5+5=0+5_&_k+1-1=0-1

k=5_____&___k=-1

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2.) If you wanted to use the **Quadratic Formula**, this is the step to look at:

k^2-4k-5=0

a=1, b=-4, c=-5
Quadratic Formula:

Solve for

and

Solve for

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