# Homework Help: Calculator, Q 17 - what it getting at

1. Apr 7, 2007

### thomas49th

What is this question going for. I can identify that OTA is a right angled triangle..... Where do I go from

2. Apr 7, 2007

### cristo

Staff Emeritus
Pythagoras?

3. Apr 7, 2007

### thomas49th

$$(x+8)(x+8) = x^{2} + (x+5)(x+5)$$

$$x ^ {2} + 16x + 64 = x^4+10x+25$$

take LHS from RHS

$$x^{2} - 6x - 39 = 0$$

but how did you know to use pythagerous?

4. Apr 7, 2007

### arildno

What relationships DO you know hold for right-angled triangles that might come in handy?

5. Apr 7, 2007

### cristo

Staff Emeritus
Sorry, one correction to your second line.

$$x ^ {2} + 16x + 64 = 2x^2+10x+25$$

Well, you did the hard part; spotting that it was a right angled triangle. Pythagoras' theorem holds for right angled triangles, and is a relationship relating the squares of the sides. Since the solution contains an x^2, this is quite a big hint as to what you should use.