Question

If 2a + 3b = 21 and ab = 15 evaluate
i) 4a2 + 9b2 ii) 4a2-962
iii)8a3 + 27b
iv)8a - 27b​

Answer 1

Answer:

solved

Step-by-step explanation:

(2a - 3b)² = (2a +3b)² - 24ab = 21² - 24×12 = 153

(2a - 3b) = √153

i) 4a² + 9b² = ( 2a + 3b )² - 12ab = 21² - 12x15 = 9 (9×7² - 20) = 9×421 = 3789

ii) 4a²-9b²  = ( 2a + 3b )( 2a- 3b ) = 21√153

iii)8a³ + 27b ³ = ( 2a + 3b ) ( 4a² + 9b² - 6ab) = 21(3789 - 90) = 77679

iv)8a³ - 27b³​ =  ( 2a - 3b ) ( 4a² + 9b² + 6ab) = √153(3789+ 90) = 3879√153

Answer 2

Answer is in the attached image

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