SOLUTION: How do I write an equation y=-3/5x+4 in standard form? And also how do i write an equation if x is 3 and y is 18 when x and y vary directly. then find the value of y when x is 7. W

Algebra ->  Linear-equations -> SOLUTION: How do I write an equation y=-3/5x+4 in standard form? And also how do i write an equation if x is 3 and y is 18 when x and y vary directly. then find the value of y when x is 7. W      Log On


   

Question 173352: How do I write an equation y=-3/5x+4 in standard form? And also how do i write an equation if x is 3 and y is 18 when x and y vary directly. then find the value of y when x is 7. What does directly and indirectly mean?????
Answer by Mathtut(3670) About Me  (Show Source):
You can put this solution on YOUR website!
standard form is Ax+By=C........so
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y=%28-3%2F5%29x%2B4...given
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5y=-3x%2B20multiply all terms by 5
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highlight%283x%2B5y=20%29
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direct variations simply means that if one variable increases then so does the other and takes the form a/b=k
inverse(or indirectly) variations mean that if one variable increases the other will decrease and vice versa....and takes the form (a)(b)=k
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so in our case x varies directly as y.... 3/18=k or 1/6=k....so when you trying to find y given x at 7.....7/y=1/6...cross multiply
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y=42.......so as x increased from 3 to 7 ....y increased from 18 to 42.....and they will aways reduce to the constant of k= 1/6
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