Evaluating Expressions with Two Variables

u09_l1_t1_we2 Evaluating Expressions with Two Variables

We're asked to evaluate the expression a squared plus ten b minus eight when a is equal to seven and b is equal to negative four.

So to evaluate the expression we really just need to substitute a with 7 and substitute b with negative 4.

Because they are saying evaluate it when a is seven and b is negative four. So let's do that.

So everywhere we see an a in the expression we should put a seven there. So instead of a squared

we should write seven squared plus ten times b. But instead of a b there we are

now going to substitute it with b is equal to negative four. So ten times negative four instead of the

b right over there. And then we have the minus eight. And now we just have to evaluate this thing.

Seven squared is forty-nine. And then ten times negative four, remember order of operations.

Multiplication comes before addition so we have to multiply this. Ten times negative four is

negative forty. So it's plus negative forty, and then we have minus eight over here.

And so we get forty-nine plus negative forty, which is the same thing as forty-nine minus forty, is going

to be nine. Then we're going to subtract eight from that. And so we get one.

Forty-nine minus forty is nine, and minus eight is one. We are done.

We have evaluated the expression when a is equal to seven and b is equal to negative four.