# Thread: Simplyfing a simple equation: (18 - 2a)^2

1. ## [Solved] Simplyfing a simple equation: (18 - 2a)^2

This is what I need to Simplify: (18 - 2a)²

The lecturer briefly mentioned that (18 - 2a)² = 18 x 2a², but I think he made an error? I don't know how he got to that answer. Substituting a value for "a" afterwards shows that it's wrong.

This is what I've done, using what I thought were normal techniques, but again substituting values for "a" afterwards shows that it's wrong too:

(18 - 2a)²
= (18 - 2a)*(18 - 2a)
= 18(18 - 2a) - 2a(18 - 2a)
= 324 - 36a - 36a + 2a².
= 324 - 72a + 2a².

Any help appreciated.

Thanks

2. Originally Posted by Timo
This is what I need to Simplify: (18 - 2a)²

The lecturer briefly mentioned that (18 - 2a)² = 18 x 2a², but I think he made an error? I don't know how he got to that answer.

This is what I've done, using what I thought were normal techniques, but again substituting values for "a" afterwards shows that it's wrong:

(18 - 2a)²
= (18 - 2a)*(18 - 2a)
= 18(18 - 2a) - 2a(18 - 2a)
The next step is
= 324 - 36a - 36a + 4a².

Thats the only mistake

3. you are suppose to get:

$(18-2a)^2
= 18^2 - 72a + 4a^2
= 324 - 72a + 4a^2
$

4. Nailed it! Thanks ever so much, both.

Means the lecturer was way out, too.

Cheers!