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kushashwa ravi shrimali Grade: 9
        

if a-b=3 and a3 -b3=117 ,then what is the value of a+b

6 years ago

Answers : (2)

Nehal Wani
21 Points
										

a-b=3


Cubing both sides, we get:


a3-b3-3ab(a-b)=27


117-3ab(3)=27


-9ab=-90


ab=10


a3-b3=(a-b)(a2+b2+ab)


117=3[(a+b)2+ab]


39=(a+b)2+10


(a+b)2=40


a+b=±7

6 years ago
annabeth
13 Points
										
a3-b3=(a-b)(a2+ab+b2)
a-b=3
a3-b3=117
117=(3)[(a-b)2+3ab]
117=(3)[(3)2+3ab]
39=9+3ab
30=3ab
10=ab
(a+b)2=(a-b)2+4ab
(a+b)2=(3)2+40
(a+b)2=49
taking sqaure root on both sides
a+b=49
 
 
9 months ago
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