Question

Using the identity: (a - b)² = a² + b² - 2ab, find the value of (991)²​

Answer 1

(991)²

Using Identity

• (a - b)² = a² + b² - 2ab

Solution :

(1000 - 9)²

• a = 1000
• b = 9

☯ Substuting the values

(1000 - 9)² = (1000)² + (9)² -2 × (1000) × (9)

(991)² = 1000000 + 81 - 2000 × 9

982081 = 1000081 - 18000

982081 = 982081

☯ LHS = RHS

Answer 2

Answer:

➮ TO FIND:

⭑(991)²

➮ USING IDENTITY:

⭑(a - b)² = a² + b² - 2ab

➮ CALCULATION:

⭑(991)²

It can be written as

(1000 - 9)²

a = 1000

b = 9

⭑Putting value of a = 1000 and value of b = 9 in the Identity: (a - b)² = a² + b² - 2ab

(1000 - 9)² = (1000)² + (9)² - 2 (1000) (9)

(991)² = 1000000 + 81 - 2000 × 9

982081 = 1000081 - 18000

982081 = 982181

L.H.S = R.H.S