Plug in & Evaluate Expression

[Iceycold12]

Hey.

Evaluate: x^2-5(3x-12) for x=10

Plug in: 10^2-5(3(10)-12) -> 100-5(30-12)

Now I forgot something here (2 1/2 months of no Algebra is definitely showing it's side effects)

Do you know simplify the parenthesis to (18) (30-12) and then multiply by -5 by 18 so it ends up as 100-90 = 10 or do I distribute the -5 the moment I evaluate for the 10 I plugged in (3(10)-12), so 100-5(30-12) distribute the -5 to both, so it simplifies to 100--150+60 -> 100+150+60 = 310. Another attempt I gave it at it which I'm most certain is wrong is simplify (3(10)-12) to (30-12) then remove the parenthesis so it's just one straight add & subtract problem but I highly doubt just removing the parenthesis is the right step to take: 100-5+30-12.

Thanks, if you need me to explain better just let me know.

 

[soroban]

Hello, Iceycold12!

Another approach . . .

\(\displaystyle \text{Evaluate: }\: x^2-5(3x-12)\;\text{ for }x=10\)

\(\displaystyle \text{Simplify first: }\: x^2 - 15x + 60\)

\(\displaystyle \text{Substitute: }\:10^2 - 15(10) + 60 \;=\;100 - 150 + 60 \;=\;10\)

 

[HallsofIvy]

Hey.

Evaluate: x^2-5(3x-12) for x=10

Plug in: 10^2-5(3(10)-12) -> 100-5(30-12)

Now I forgot something here (2 1/2 months of no Algebra is definitely showing it's side effects)

Do you know simplify the parenthesis to (18) (30-12) and then multiply by -5 by 18 so it ends up as 100-90 = 10 or do I distribute the -5 the moment I evaluate for the 10 I plugged in (3(10)-12), so 100-5(30-12) distribute the -5 to both, so it simplifies to 100--150+60 -> 100+150+60 = 310. Another attempt I gave it at it which I'm most certain is wrong is simplify (3(10)-12) to (30-12) then remove the parenthesis so it's just one straight add & subtract problem but I highly doubt just removing the parenthesis is the right step to take: 100-5+30-12.

This is incorrect because the "30- 12" is MULTIPLIED by -5, not added to it.
-5(30- 12)= -5(30)-5(-12)= -150+ 60= -90 and then you have 100- 90= 10.

Thanks, if you need me to explain better just let me know.