Hi there!
To solve is pretty easy. First, simplify.
21/4=(1/2x+3x) -> Combine Like Terms
21/4=7/2x
FLIP
7/2x=21/4
Multiply both sides by 2/7.
(2/7)*(7/2x)=(2/7)*(21/4)
x = 2/3
Hope this helps!
It is not differentiable at x=1 since the slope of the tangent line as x -> 1 from the right is 1 while the slope of the tangent line as x->1 from the left is -1
Multiples of 7: 7,14,21,28,35, 42.....
The interior angles of a triangle add up to 180 degrees, therefore:
40 + 40 + x-10 = 180
80 + x - 10 = 180
70 + x = 180
x = 110
< D = 110 - 10 = 100