Question

if a-b = 7 and ab=18 :, find a plus
b​

Answer 1

Answer:

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Step-by-step explanation:

$a - b = 7 \\ = > a = b + 7$

put the value of a in ab = 18

$ab = 18 \\ = >( b + 7)(b) = 18 \\ = > {b}^{2} + 7b - 18 = 0 \\ = > {b}^{2} + 9b - 2b - 18 = 0 \\ = > b(b + 9) - 2(b + 9) = 0 \\ = > (b - 2)(b + 9) = 0 \\ = > b = 2, - 9$

The positive value of b = 2

The negative value of b = -9

the value of a is

$a - b = 7 \\ = > a - (2) = 7 \\ = > a = 7 + 2 = 9 \\ = > a = 9 \\ or \\ = > a - b = 7 \\ = > a - ( - 9) = 7 \\ = > a = 7 - 9 = - 2 \\ = > a = - 2$

So, the Positive value of a = 9

So, the negative value of a = -2

Answer 2

Step-by-step explanation:

a - b = 7

∴ a = 7 + b                                                         (1)

ab = 18

∴ (7 + b)b = 18

∴ b^2 + 7b - 18 = 0

∴ b^2 -9b + 2b -18 = 0

∴ b(b - 9) + 2( b - 9) = 0

∴ (b-2)(b-9) = 0

∴ b = 2,9

∴ a - 9 = 7

∴ a = 16 but 16 *9 ≠ 18 so b is 2

∴ a - 2 = 7

a = 9

a + b = 9 + 2 = 11

hope it helps :)