Question

The value of 21² is?

• A. 220+221
• B. 219+220
• C. 218+219
• D. 217+218

Answer 1

The correct option is A

220+221

${21}^2$ = $(20+1{)}^2$
Now we will use the algebraic identity $(a+b{)}^2=a^2+2ab+b^2$
= ((20)² + 2x20x1 + (1)²)
= (400 + 40 + 1)
= 441