Question

31x19 with formula simply and eazy

Answer 1

Answer:

589

Step-by-step explanation:

(30+1) × (20 -1)

30×20-30+20-1 {using distributive property}

600-11

=589

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Answer 2

31 × 19

Find : Using identity

Identity to use : (x+a) × (x+b) = x² + x(a+b) + (a×b)

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(20+11) × (20-1)

(20+11) × [20+(-1)]

x = 20

a = 11

b = (-1)

substituting the values,

(20)² + 20[11+(-1)] + [(11) × (-1)]

400 + 20(10) + (-11)

400 + 200 + (-11)

600 + (-11)

589

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SOME MORE FORMULAS:

(a+b)² = a² + 2ab + b²

(a-b)² = a² - 2ab + b²

a² - b² = (a+b)(a-b)

(a+b+c)² = a² + b² + c² + 2ab + 2bc + 2ca

(a+b)³ = a³ + 3a²b + 3ab² + b³

(a-b)³ = a³ - 3a²b + 3ab² - b³

a³+b³ = (a+b)(a² - ab + b²)

a³-b³ = (a-b)(a² + ab + b²)

a³ + b³ + c³ = (a+b+c)(a²+b²+c² - ab - bc - ca)

Conditional identity :

a³ + b³ + c³ = 3abc

if a + b + c = 0

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