19. (a)If x2 + 1/x2 = 18 , find the value of x3 + 1/x3 .
(b) If x – y = 5 and xy = -6 , find the value of x3 – y3.
Answers
Answered by
4
(b) x-y = 5
x= 5+y
equation (2) xy = -6
(5+y)×y =-6
5y +y2 =-6
y2 + 5y +6 =0
y2+3y +2y +6 =0
y(y+3) +2(y+3) =0
(y+3) (y+2)=0
y can be -3 and -2
x=5+(-3) =2 and 5+(-2) =3
x3-y3 can be (2)3 -(-3)3=
8-27=
(-19) and
(3)3 -(-2)3
27+8 =35
x= 5+y
equation (2) xy = -6
(5+y)×y =-6
5y +y2 =-6
y2 + 5y +6 =0
y2+3y +2y +6 =0
y(y+3) +2(y+3) =0
(y+3) (y+2)=0
y can be -3 and -2
x=5+(-3) =2 and 5+(-2) =3
x3-y3 can be (2)3 -(-3)3=
8-27=
(-19) and
(3)3 -(-2)3
27+8 =35
Similar questions