MathRevolution wrote:
(1+√3+√5)^2 - (√3+√5)^2=?
A. 1+2√3+2√5
B. 1+2√3+3√5
C. 1-√3+√5
D. 1+√3-√5
E. √3+√5
Another approach:
For test day, everyone should know the following
approximations:
√2 ≈ 1.4
√3 ≈ 1.7
√5 ≈ 2.2
So, (1+√3+√5)² - (√3+√5)² ≈ (1+ 1.7 + 2.2)² - (1.7 + 2.2)²
≈ (4.9)² - (3.9)²
≈ 25 - 16
≈
9Now check the answer choices....
A. 1+2√3+2√5 ≈ 1 + 2(1.7) + 2(2.2) ≈
8.8. CLOSE - KEEP
B. 1+2√3+3√5 ≈ 1 + 2(1.7) + 3(2.2) ≈
11. ELIMINATE
C. 1-√3+√5 ≈ 1 - 1.7 + 2.2 ≈
1.5. ELIMINATE
D. 1+√3-√5 ≈1 + 1.7 - 2.2 ≈
0.4. ELIMINATE
E. √3+√5 ≈ 1.7 + 2.2 ≈
3.9. ELIMINATE
Answer:
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