Question

√21-4√5+8√3-4√15) is equal to what .please answer it

Answer 1

≡≡≡≡≡≡≡≡≡≡≡≡≡≡

    ANSWER

≡≡≡≡≡≡≡≡≡≡≡≡≡≡

Expand (a + b√3 + c√5)^2  

= (a^2 + 3b^2 + 5c^2) + 2ab√3 + 2ac√5 + 2bc√15  

equate coefficients to get  

ab = 4, ac = -2, bc = -2  

either (a,b,c) = (2,2,-1) or (-2,-2,1)  

Verify that a^2 + 3b^2 + 5c^2 = 21  

So the square root is  

2 + 2√3 - √5