Evaluate Using Identities: 81²-79²
Answers
Answered by
1
Answer:
=320
Step-by-step explanation:
(81*81) - (79*79)
=320
Answered by
2
Answer:
320
Step-by-step explanation:
81² - 79²
= (80 + 1)² - (80 - 1)²
= According to Identity: (a + b)² - (a - b)² = 4ab
= 4(80)(1)
= 320
This is the simplest way to solve such questions
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Proof for (a + b)² - (a - b)² = 4ab
(a + b)² - (a - b)² = 4ab
(a² + b² + 2ab) - (a² + b² - 2ab) = 4ab
Opening the brackets,
a² + b² + 2ab - a² - b² + 2ab = 4ab
2ab + 2ab = 4ab
4ab = 4ab
LHS = RHS
Hence proved.
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