Consider the straight line and be the inclination of the straight line as shown in the given diagram now the slope of the represented by . Let be any point on the given line . Let be the X-intercept of the straight line, so the line must passes through the point .

Take as X-intercept of the straight line so the line must passes through the point , i.e. X-intercept. From point draw perpendicular on -axis.

Now from the given diagram, consider the triangle , i.e. , by the definition of slope we take

Now by definition we can use instead of , we get

Which is the equation of straight line having slope and X-intercept .

__NOTE__**:** It may be noted that if the line passes through the origin , then take X-intercept is equal to zero i.e. , so the equation of straight line becomes .

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__Example__**:** Find the equation of straight line having slope and X-intercept is equal to.

Here we have slope and X-intercept

Now using the formula of straight line having slope and X-intercept

Substitute the above values in the formula to get the equation of straight line

Which is the required equation of straight line.