Question

Can you do this fast by using formula?Please fast. All three..

Answer 1

Hi ,

x - y = 7 ----( 1 )

x³ - y³ = 133 -----( 2 )

We know the algebraic identity

( x - y )³ = x³ - y³ - 3xy( x - y )

7³ = 133 - 3xy × 7

343 = 133 - 21xy

21xy = 133 - 343

21xy = -210

xy = -210 / 21

xy = -10

I hope this helps you.

:)

Answer 2

(x - y)³ = x³ - y³ - 3xy(x - y)
7³ = 133 - 3xy × 7
343 = 133 - 21xy
21xy = 133 - 343
21xy = -210
xy = -210 / 21
xy = -10

Therefore, (i)xy = -10

(x+y)² = (x-y)²+4xy
(x+y)² = 7² + 4(-10)
(x+y)² = 49 - 40
x+y = √9
x+y = ±3

(x+y)² = x²+y²+2xy
3² = x²+y² + 2(-10)
x²+y² = 9+20
x²+y² = 29

If we take x = -3 also, x²+y² = 29