f(x) = 3x-7 and g(x)= -2x-6. Find (f * g)(4) .
Please help. I don't know nothing about math. I can solve problems but have no idea how to set them up!

Question

f(x) = 3x-7 and g(x)= -2x-6. Find (f * g)(4) . 
Please help. I don't know nothing about math. I can solve problems but have no idea how to set them up!

anonymous · Answer

@campbell_st

campbell_st · Answer

so you need to multiply f and g

(f*g)(x) = (3x -7)(-2x - 6)

so you need to multiply the 2 binomials as the 1st step

does that make sense..?

anonymous · Answer

3x * -2x & -7 * -6?

-6x * 42 ?

campbell_st · Answer

not quite it can be split into $$3x(-2x - 6) -7(-2x - 6)$$

can you distribute and collect like terms..?

anonymous · Answer

-6x - 18x + 14x + 42 ?
I know how to collect like terms, but not distribute.

campbell_st · Answer

great except the -6x should be -6x^2

campbell_st · Answer

so that would mean that 

$$f*g(x) = -6x^2 - 4x + 42 $$

now just substitute x = 4 and calculate an answer

anonymous · Answer

Wait, so -24 - 12 + 42
or would it be -96 - 12 + 42?

campbell_st · Answer

no its 

$$(f*g)(4) = -6 \times 4^2 - 4 \times 4 + 42$$

anonymous · Answer

-70? Isn't that the same as -96 - 12 + 42?

campbell_st · Answer

well it's almost right

-96 - 16 + 42 = ?

you middle term was incorrect

campbell_st · Answer

lol... sorry just realised your answer was correct... and it was a typo

anonymous · Answer

Lol, it was my mistake! Thank you so much!