2
$\begingroup$

Please refer to image for explanation.

enter image description here

$\endgroup$
3
$\begingroup$

Consider this blue triangle:

enter image description here

The area of the combined rectangle is $(a+b)h$ so the area of the large blue and red right-angled triangle is half this, namely $\frac12(a+b)h$

The area of the small rectangle on the left is $ah$ so the area of the small red right-angled triangle on the left is half this, namely $\frac12ah$

So the area of the blue triangle is the difference in area between the two right-angled triangles, namely $\frac12(a+b)h-\frac12ah = \frac12bh$, i.e. half of base times height

$\endgroup$
  • $\begingroup$ Thank you, Henry, I haven't practised maths for a long time, and was feeling paralysed. The diagram simplifies the problem wonderfully. $\endgroup$ – Dave Kirkby Jan 19 at 10:49

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.