Formula used here :

a) 202×205

it can also be written as :200+2 ×200+5

=>(200+2)(200+5)

it is in the form of (x+a)(x+b)

here,x=200 ,a=2 and b =5

=>(200)²+(2+5)200+(2×5)

=>40,000+7×200+10

=>40,000+1400+10

=>41410

∴202×205=41410

b)99²

=>(100-1)²

it is in the form of.(a-b)² where ,a=100 and b=1

=> (100)²+(1)²-2(100)(1)

=>10,000-200+1

=>9800+1

=>9801

∴99²=9801

Verified answer

Answer:

a) (200+2)(200+5)= 200^2 +(2+5)200+(2×5)= 40000+ 1400+10= 41410 b) (90+9)^2 = 90^2+9^2+2×90×9= 8100+81+1620 = 9801

Explanation:

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