anyone good at maths?

Question

Find the equation of the straight line that it parallel to y + 20x = 90 and passes through the point 4, -10. 
im just looking over it so i went on some online plotter thing and put it in and y + 20x = 90 passes through 4, -10 so how can a line parallel also pass through that point?
also can someone explain what the whole = 90 bit is about i dont get how that can equal 90 or what that means or does or whatever

Anonymous · Accepted Answer

In slope/intercept form, the equation is y = -20x + 90 which means the slope is -20 and the y-intercept is 90.

A parallel line will be y = -20x + b 

 -10 = (-20)(4) +b 

b = 70

Line is y = -20x + 70

Caleb F · Answer

Parallel lines have the same slope.
In the first equation y + 20x = 90 rearrange it into slope-intercept form (y = mx + b, where m is the slope and b is the y intercept)

y = -20x + 90     The slope is -20; the y-intercept is 90

So in the new equation, y = -20x + b.  To find b and finish the problem, use the equation:
(y-y1) = m(x-x1) where x1, y1 is the point you are given that the line is crosses through.

y-(-10) = -20(x-4)
y + 10 = -20 x + 80
y = -20x + 70   is your final answer

The 90 part is just something that tells you where on the graph the line is located.  The coefficients on the variables help you find the slope, but you have to know where to start from.  Usually you would put the equation into slope intercept form like I did, and then the y-intercept is the place at which the line crosses the y-axis.

CubicleWizard · Answer

first you must put the equation in the standard form 
y=bx+c so y=-20x+90

so if // the slope is the same at -20 

  the x axis at y =0 = 90/20 ;  at x=0 y =90

For the // line  it can't cross point 4 -10 as that gives a slope of -20/8

your problem is not correctly defined

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anyone good at maths?

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