Question

a-b = 7 and ab= 18 ; find a+b

Answer 1

a=7+b and a=18/b then equal the equation and solve for the value of b and find the value of a with the help of value of b

Answer 2

↑ Here is your answer ↓
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Given that,

$ab = 18$

$b = 18/a$

Now sub in the other equation,

$a - b = 7$

$a - 18/a = 7$

Multiply throughout by 'a',

$a^2 - 18 = 7a$

$a^2 - 7a - 18 = 0$

Lets solve this quad. equation now,

$a^2 - 9a + 2a - 18 = 0$

$a(a-9) + 2(a-9) = 0$

$(a+2)(a-9) = 0$

So,

$a = 9$

Now sub it again somewhere to find 'b',

$b = 18/a$

$b = 18/9$

$b = 2$

Now finally,

$= a + b$

$= 9+2$

$= 11$

Cheers! :)