Video Transcript
Which of the following equations
represents a straight line? (A) 𝑦 equals root 𝑥 plus six, (B)
𝑦 plus one over 𝑥 equals negative eight, (C) 𝑥 plus root 𝑦 equals negative five,
or (D) negative seven 𝑥 minus two 𝑦 equals negative nine.
So to enable us to decide which one
of these is in fact the correct equation to represent a straight line, what we’re
gonna do is look at a couple of the general forms for the equation of a straight
line. Well, the couple of forms that
we’ve got here are the standard form, 𝐴𝑥 plus 𝐵𝑦 equals 𝐶, or we have the
point-slope form, which is 𝑦 minus 𝑦 sub one equals 𝑚 multiplied by 𝑥 minus 𝑥
sub one.
Well, one thing we can notice from
both of our forms is the fact that we have here 𝑥 to the power of one and then 𝑦
to the power of one. And that’s in the standard
form. And then in the point-slope form,
we also have 𝑦 to the power of one or 𝑥 to the power of one. So therefore, with this bit of
information and the two forms we have here for the equation of a straight line,
let’s have a look at the four equations that we have to see if they in fact
represent a straight line.
Well, if we look at equation (A),
what we have is root 𝑥. Well, if we write this in exponent
form, this is 𝑥 to the power of a half. So therefore, this cannot be the
correct answer cause this will not represent a straight line.
Well, in equation (B), what we have
is one over 𝑥. Well, if we rewrite this in
exponent form, this is 𝑥 to the power of negative one. So therefore, once again, this
cannot be the correct answer. And it cannot be a straight line
because we don’t have the 𝑥 to the power of one, 𝑦 to the power of one.
Then, if we take a look at (C),
once again, we’ve got a root, and this time it’s root 𝑦. So therefore, this is gonna be 𝑦
to the power of a half. So therefore, this can’t be the
correct equation either.
But if we check equation (D), what
we have here is 𝑥 to the power of one and 𝑦 to the power of one. So therefore, this can be the
correct equation. So this could be the equation of a
straight line. And what we can also notice is that
it takes the standard form for the equation of a straight line, and that is 𝐴𝑥
plus 𝐵𝑦 equals 𝐶. So therefore, we can say that the
equation which represents the straight line is negative seven 𝑥 minus two 𝑦 equals
negative nine. And it’s in the standard form 𝐴𝑥
plus 𝐵𝑦 equals 𝐶, where 𝐴 is equal to negative seven, 𝐵 is equal to negative
two, and 𝐶 is equal to negative nine. Okay, great, so we’ve solved this
problem.
