Question

if a+b=5 and 1/a+1/b=3 then a³+b³=?​

Answer 1

Answer:

a+b=5                               equation 1

1/a + 1/b = 3                       taking lcm

(a+b)/ab =3                        putting a+b value from equation 1

5/ab =3                              cross multiplication

5/3 = ab                             equation 2

in equation one squaring on both side we get

a² + b² + 2ab = 25              puting value of ab

a² + b² = 25 - 2*5/3

a² + b² = (75-10)/3

a² + b² = 65/3                       equation 3

so

a³ + b³ = (a+b)(a²+b²-ab)      now putting value from equation 1,2 and 3

5*(65/3 - 5/3)            

5*(60/3)

5*20

100

Step-by-step explanation:

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