Question

d) If a + b2 = 9 and ab = 4.
Find the value of 3(a + b)2 - 21a - b)?.​

Answer 1

Step-by-step explanation:

Here a-b=2

Here a-b=2And ab=4

Here a-b=2And ab=4Now (a+b)^2=(a-b)^2+4ab

Here a-b=2And ab=4Now (a+b)^2=(a-b)^2+4abOr, (a+b)^2=(2)^2+4×4

Here a-b=2And ab=4Now (a+b)^2=(a-b)^2+4abOr, (a+b)^2=(2)^2+4×4Or, (a+b)^2=4+16

Here a-b=2And ab=4Now (a+b)^2=(a-b)^2+4abOr, (a+b)^2=(2)^2+4×4Or, (a+b)^2=4+16Or, (a+b)^2=20

Here a-b=2And ab=4Now (a+b)^2=(a-b)^2+4abOr, (a+b)^2=(2)^2+4×4Or, (a+b)^2=4+16Or, (a+b)^2=20Or, a+b=√20

Here a-b=2And ab=4Now (a+b)^2=(a-b)^2+4abOr, (a+b)^2=(2)^2+4×4Or, (a+b)^2=4+16Or, (a+b)^2=20Or, a+b=√20Or,a+b=√(2×2×5)

Here a-b=2And ab=4Now (a+b)^2=(a-b)^2+4abOr, (a+b)^2=(2)^2+4×4Or, (a+b)^2=4+16Or, (a+b)^2=20Or, a+b=√20Or,a+b=√(2×2×5)Or, a+b=+-2√5

r, a+b=+-2√5Therefore a+b=+2√5,-2√5

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Answer 2

Step-by-step explanation:

a ²+ b² =9

ab= 4

(a+b)²=a²+b²+2.a.b

=> 9+2×4

=>17

(a-b)² = a²+b²-2.a.b

=> 9-2×4

=> 1

3(a+b)² - 2(a-b)²

=>3×17 - 2×1

=>51 - 2

=> 49