Answer:
A. 3x^2+7x^2+2×3x ×7-84x = 3x^2+7x^2-2×3x×7
9x^2+49x^2+42x-84 x= 9x^2+49x^2-42x
9x^2+49x^2-42 = 9x^2+49 x^2-42x
verified
B.
Answer:
Step-by-step explanation:
When bases are same and it is multiplication, then add the exponents.
Apply rule : 
8*10 squared as a decimal would be 2.8
Answer:
Step-by-step explanation:
A spring has a force formula of F = k*x
f = 125 N
x = 0.15 m
125 = k*0.15
k =833.33
F = ?
k = 833.33
x = 0.25 m
F = 833.33 * 0.25
F = 208.33 N
You could do this without solving for k
F1/F2 = x1/x2
F1 = 125 N
F2 = ?
x1 = 0.15
x2 =0.25
125 / F2 = 0.15 / 0.25 Cross multiply
125 * 0.25 = 0.15 * F2 Divide by 0.15
125*0.25 /0.15 = F2
F2 = 208.33 just as you got above
