Question

if 5a-2b=7 and ab =2 . find the value of( 5a+2b)²​

Answer 1

5a-2b=7 ... (1)

ab =2 ... (2)

Squaring (1)

${ (5a-2b) }^{2} = {7}^{2} \\ {(5a)}^{2} + {(2b)}^{2} - 2 \times 5a \times 2b = 49 \\ {(5a)}^{2} + {(2b)}^{2} - 20ab = 49 \\ \\ add \:20ab \: on \: both \: side \\ \\ {(5a)}^{2} + {(2b)}^{2} - 20ab + 20ab= 49 + 20ab \\ {(5a + 2b)}^{2} - 20ab = 49 + 20ab \\ {(5a + 2b)}^{2} = 49 + 40ab \\ {(5a + 2b)}^{2} = 49 + 40 \times 2 \\ {(5a + 2b)}^{2} = 129$

Answer 2

Answer:

5a-2b=7

ab=2

Step-by-step explanation:

(5a+2b)^2=(5a-2b)^2+4(5a)(2b)

                =(7)^2+4(5)(2)(ab)

                =49+4(5)(2)(2)

                =49+80

               =129