Area of a triangle using double integration

Question

What is the AREA of the triangle bounded by the lines $y=2x$ and $x=1$?

I solved it using single integration and i got $A=1$. The problem is , I do not know how to solve it using double integration.

Answer 1

Using double integration, the area is $$ \int_{0<x<1}\int_{0<y<2x} dxdy = \int_0^1 \left[\int_0^{2x} dy \right]dx =\int_0^1 \left[2x \right]dx = \left[x^2 \right]_0^1 = 1 $$