Question

If dy=(2x+1)dx and y=7 when x=1, find the value of y when x=3.

Answer 1

dy = 2 x dx + dx

y = x^2 + x + c
7 = 1 + 1 + c so c = 5
and
y = x^2 + x + 5
when x = 3
y = 9 + 3 + 5
= 17