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Students in this video, let's get started with straight lines.

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All right, well, over here we have our X and Y axis.

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Now, let me write an equation of a line I have for X plus three.

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Y is equal to 12.

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Now, this describes a straight line.

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Now, what do I mean?

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When I say that this describes a straight line, it means that every solution of this equation will

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lie on a straight line.

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For example, let's take some solutions.

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I have X, I have Y over here.

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Now you will see that when X is equal to zero, that's zero plus three, Y is equal to twelve.

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That is why it is equal to four.

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Right.

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So zero four is one solution for this equation.

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Similarly, when X is equal to three, you have twelve plus three.

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Y is equal to twelve.

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That is three.

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Y is equal to zero.

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Therefore Y is equal to zero three.

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Zero is also a solution of this equation over here.

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All right.

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Now let's plot these two points.

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I have zero for over here and I have three zero over here.

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Now, if I join these two points.

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I'll get a straight line right now when we say that this equation is a straight line, what we mean

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is that you take any point on this straight line, it will satisfy this equation.

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Similarly, you find any solution of this in this equation.

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It will lie on this line.

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So that is what we mean when we say that this equation describes a line.

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Let's take another example.

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What would the solution be when X is equal to one?

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When X is equal to one, you get four plus three, Y is equal to twelve or three.

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Y is equal to eight, or Y is equal to eight by three.

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Right over here.

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If you draw a line at X equal to one right, it will intersect.

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This line over here at Y is equal to eight by three.

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That is what we mean when we say that this describes a straight line.

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Now this is one way in which we write a straight line.

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This is the generic form.

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And let me write the generic formula here.

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That would be X plus B Y policy is equal to zero for this.

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Over here is the generic form of a straight line in the X Y plain.