# Day 7 quiz

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# Day 7:

Given the following line described by:

4y – 2x = 20,

where will it cross the y-axis?

A)  -1/2
B) 1/2
C) -5
D) 5

[/vc_column_text][vc_text_separator title=”Day 7 Answer Explanation”][/vc_column][/vc_row][vc_row][vc_column][vc_column_text]The first step is to put the equation into slope-intercept form since this makes the y-intercept (where it crosses the y-axis) explicit.  This is y = mx + b

Use algebraic manipulation to isolate y.

4y = 2x + 20

y = 4x/2 + 5

This simplifies to:

y = ½x + 5.

1/2 is the slope.

5 is the y intercept.

(A) and (B) incorrectly identify the y-intercept as the slope and (A) makes a sign error.  (C) also makes a sign error.

Therefore the correct answer is (D)[/vc_column_text][/vc_column][/vc_row][vc_row][vc_column][vc_text_separator title=”Key Math Fact To Learn” css=”.vc_custom_1486917830691{padding-top: 20px !important;}”][/vc_column][/vc_row][vc_row][vc_column][vc_column_text]

Know the slope-intercept formula backwards and forwards.

y = mx + b

Although it ‘seems easy’ there are many questions on the ACT and the SAT that require a detailed understanding of how to interpret this form of an equation.  You will use it to solve systems of equations as well as so many other types of questions.

The first step is memorizing it, the next is being able to manipulate it and transform other line equations into it, the last is being able to interpret it given strange looking equations.  Future questions will deepen your understanding of this form in detail.

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