## anonymous one year ago (8-√2)(9-√ 5)

1. zzr0ck3r

$$(a+b)(c+d)=ac+ad+bc+bd$$ $$\sqrt{a}\sqrt{b}=\sqrt{ab}$$ Try using these rules and show me what you get.

2. anonymous

72+square root of 10?

3. zzr0ck3r

You did $$(a+b)(c+d)=ac+bd$$ which is a common mistake. So common it has a name: Freshman's Dream Using the first rule I showed you, we have $$(8-\sqrt{2})(9-\sqrt{5})=8*9-8\sqrt{5}-9\sqrt{2}+\sqrt{2}\sqrt{5}$$ Now use the other rule and simplify some.