Question

15. If a+b = 7 and ab = 10; find the value of (a-b);


Chapter 3 - Algebra - RS Agarwal - ICSE - Class 9th - Exercise 3 A

Answer 1

Hey,
Use the formula,
(a+b)^2-(a-b) ^2=4ab
Put the required values,
-(a-b)^2+49 =4*10
-(a-b)^2=40-49
-(a-b) ^2=-9
a-b=3.

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Answer 2

Hey there! ☺☻☺

Given,
a+b = 7
ab = 10

We know,
 $(a+b)^2 - (a-b)^2 = 4ab\\(7)^2 - (a-b)^2 = 4\times 10\\49 - (a-b)^2 = 40\\- (a-b)^2 = 40 - 49\\(a-b)^2 = 9\\a-b = \sqrt{9} \\ a- b = \pm 3$