# Four Aligned Squares +-- {.image} [[FourAlignedSquares.png:pic]] > The area of the bottom left square is $5$. What's the area of the blue triangle? =-- ## Solution by [[Area of a Triangle]] +-- {.image} [[FourAlignedSquaresLabelled.png:pic]] =-- With the points labelled as above, $C D$ is [[parallel]] to $I G$, so the area of triangle $I G D$ is the same as of $I G C$. The total area of rectangle $A C F H$ is $6 \times 5 = 30$. Triangle $G F C$ is half of square $G B C F$ so has area $10$. Triangle $I A C$ is half of rectangle $I A C E$ so has area $7.5$. Finally, triangle $H G I$ has area $2.5$. So the shaded triangle has area $30 - 10 - 7.5 - 2.5 = 10$.