Answer: 7x^2+21x+14
Step-by-step explanation:
(7x+7)(x+2)
Multiply each term in the first parentheses by each term in the second parentheses (FOIL)
7x×x+7x×2+7x+7×2
↘ ↙
7x×x calculate product
7x^2+7x×2+7x+7×2
↘ ↙
7x×2 calculate product
7x^2+14x+7x+7×2
↘↙
7×2 multiply numbers
7x^2+14x+7x+14
↘ ↙
21x collect like terms
7x^2+21x+14 is your end result.
The derivative of f(x) at x=3 is 2x=6 approaching from the left side (apply power rule to y=x^2). The derivative of f(x) at x=3 is m approaching from the right side. In order for the function to be differentiable, the limit of derivative at x=3 must be the same approaching from both sides, so m=6. Then, x^2=mx+b at x=3, plug in m=6, 9=18+b, so b=-9.
The width should be 32 inches.
Answer : 
(1) 
Use FOIL method to mulitply (3x – 5)(3x – 5)
(2) 
Use FOIL method to mulitply (3x - 5)(3x + 5)
(3) 
Use FOIL method to mulitply -(3x + 5)(3x + 5)
(4) 
Use FOIL method to mulitply -(3x + 5)(3x - 5)
So equation 2 is true
