If ab = 15 and a^2 + b^2 = 40, then find (a + b)^4 - (a - b)^4.
i got 4800
ab = 15
a^2 + b^2 = 40
[ (a + b)^4 - ( a - b)^4 ] =
[ ( a + b)^2 + ( a - b)^2 ] [ (a + b)^2 - ( a - b)^2 ] =
[ a^2 + b^2 + a^2 + b^2 ] [ a^2 + b^2 - a^2 - b^2 + 4ab ] =
[ 2 (a^2 + b^2) ] [ 4ab ] =
[ 2 (40) [ * [ 4(15) ] =
[ 80 ] * [ 60 ] =
4800