Question

pls answer fast
help me​

Answer 1

Step-by-step explanation:

(a) { a^2 - b^2 = (a+b) (a-b) } ( Identity)

34^2-21^2 = (34+21)(34-21)

= (55)(13)

= 715 Answer

(b) a = 5-2√5

a^2 = (5-2√5)^2

= (5)^2 + (2√5)^2 - 2×5×2√5

{ ( a - b )^2 = a^2 + b^2 - 2ab } ( Identity)

= 25 + 4×5 - 20√5

= 25 + 20 - 20√5

= 45 - 20√5

= 5(9 - 4√5) Answer

Note : When we do square of a number which is in root the square got cancelled with the root .

Thanks