Question

If 5x-2y = 15 and xy = 20, find the value of 25x²+ 4y² and (5x+2y)²​

Answer 1

Answer:

5x-2y=15

squaring on both sides

(5x)²+(2y)²-2(5x)(2y)=(15)²

25x²+4y²-10(20)=225

25x²+4y²=225+200

25x²+4y²=425

Answer 2

Consider the given equation,

5x−2y=7 and xy=2

We have to find (5x+2y) ²

Now,

(5x−2y) ² =25x 2 +4y 2 −20xy7 2=25x 2 +4y−20×225x 2 +4y 2 =89

Now,

(5x+2y) ^2 =25x 2 +4y 2 −20xy(5x+2y)

2

=89−20×2

(5x+2y) 2 =49

Hence, this is the answer. 49