(2 sqrt 3 + sqrt5 ) (2 sqrt 3 - sqrt 5)

[ginny1029]

help lol

if it were just the sqrt's i would square them but I dont know what to do with the first 2's

[Subhotosh Khan]

help lol

if it were just the sqrt's i would square them but I dont know what to do with the first 2's --- square those too

(2\sqrt{3} )^2 \, = \, 2^2 \cdot (\sqrt{3})^2



I suppose you need to evaluate:

(2\sqrt{3} \, + \, \sqrt{5})\cdot (2\sqrt{3} \, - \, \sqrt{5})

then use

(a + b)\cdot (a-b) \, = \, a^2 \, - \, b^2

[ginny1029]

ok so how would i write it

(2 sqrt 3)^2 times (sqrt 5)^2

(4 x 3) - (5)

12-5

7

??

[Subhotosh Khan]

ok so how would i write it

(2 sqrt 3)^2 times (sqrt 5)^2 <<< Why is that???

(4 x 3) - (5)

12-5

7 <<< Correct answer

??