If y is directly proportional to x^2 and the difference in the values of y when x = 1 and x = 3 is 32, find the value of y when x = -2
Please show the way step by step. Thank you
Help me math problem about direct proportional (5*)?
2016-08-01 9:16 am
回答 (2)
2016-08-01 9:27 am
✔ 最佳答案
y ∝ x²Then y = k x²
where k is a non-zero constant.
The difference in the values of y when x = 1 and x = 3 is 32 :
k (3)² - k (1)² = 32
8k = 32
k = 4
Then, y = 4 x²
When x = -2 :
y = 4 * (-2)²
y = 16
2016-08-01 9:29 am
y ∝ x²
Hence, y = kx²
With x = 1, we have y = k and with x = 3 we have y = 9k
so, 9k - k = 32
i.e. 8k = 32
=> k = 4
Therefore, y = 4x²
so, when x = -2 we have:
y = 4(-2)² => 16
:)>
Hence, y = kx²
With x = 1, we have y = k and with x = 3 we have y = 9k
so, 9k - k = 32
i.e. 8k = 32
=> k = 4
Therefore, y = 4x²
so, when x = -2 we have:
y = 4(-2)² => 16
:)>
收錄日期: 2021-04-18 15:24:58
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