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If 4x2 + y2 = 40 and xy = 6, then find the value of 2x + y.
6
8
5
4
Let’s break it down:
- We’re given two equations:
1. \( 4x^2 + y^2 = 40 \)
2. \( xy = 6 \)
- We want to find out what \( 2x + y \) equals, and check the options.
Let’s do a quick solve:
- From \( xy = 6 \), we can say \( y = \frac{6}{x} \).
- Plug \( y \) into the first equation:
\( 4x^2 + \left(\frac{6}{x}\right)^2 = 40 \)
\( 4x^2 + \frac{36}{x^2} = 40 \)
- Multiply both sides by \( x^2 \):
\( 4x^4 + 36 = 40x^2 \)
\( 4x^4 - 40x^2 + 36 = 0 \)
Let \( u = x^2 \):
\( 4u^2 - 40u + 36 = 0 \)
- Divide by 4:
\( u^2 - 10u + 9 = 0 \)
- Factor or use quadratic formula:
Roots are \( u = 9 \) and \( u = 1 \), so \( x^2 = 9 \) or \( x^2 = 1 \).
So \( x = 3 \) or \( -3 \), and \( x = 1 \) or \( -1 \).
Let’s check each:
Case 1: \( x = 3 \), \( y = 2 \):
\( 2x + y = 2*3 + 2 = 6 + 2 = 8 \)
Case 2: \( x = 1 \), \( y = 6 \):
\( 2x + y = 2*1 + 6 = 2 + 6 = 8 \)
Other combinations either go negative or repeat the results.
So the answer is 8.
- Option 1: 6—not right.
- Option 2: 8— This is the correct answer.
- Option 3: 5—nope.
- Option 4: 4—also not correct.
By: Parvesh Mehta ProfileResourcesReport error
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