Question

How to solve f(-3)= -2x^2+5x

Answer 1

Replace all the x values with -3 

f(-3)=-2(-3)^2+5(-3) 
f(-3)=2(9)-15
f(-3)=18-15 
f(-3)=3 

Hope I helped :) 

Answer 2

Plug -3 in for x. the equation should look like this
f(-3)=-2(-3)^2+5(-3)

simplify by multiplying and you get
f(-3)=6^2-15

now apply the exponent
f(-3)=36-15

finish it off by subtracting and you get
f(-3)=21