act math tips: the one equation of a line you need to know

https://www.youtube.com/watch?v=qm_dittat-8&feature=youtu.be

in geometry class, there are several forms of an equation of a line that most students learn.

you learn standard form, slope-intercept form, point-slope form, etc., but for basically every single question that the act math section asks you about lines on a coordinate plane, there’s only one you really need to know. only one that is really useful.

the winner is…slope-intercept form, or .

ding! ding! ding!

slope-intercept form is so useful because, in order to answer many questions on the act, you will need to find: either the slope or the y-intercept, or you will be given the slope and a point and need to find the y-intercept, or something along those lines.

if you put an equation in slope-intercept form,, you will see this information instantaneously. in the equation :

• m is the slope.
• b is the y-intercept

so if an equation of a line is in this form, you don’t need to do any extra work to determine what these values are.

the act knows how powerful slope-intercept form is, so it will rarely give you an equation in this form. instead, it will typically give lines in standard form, ax + by = c. so what you want to do, in most cases, is use your algebra skills to move this equation around to slope-intercept form.

let’s say you have this equation of a line: . move it around so that you have the y isolated on one side:

• 
• 
• 
• 
• 

now we can see that the slope of this line is and the y-intercept is 3, and that’s very valuable information.

check out the video above for examples on how this works in real act-like problems!