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pochemuha
2 years ago
9

Find an equation of a line through (2, 1) and perpendicular to - 2x + 4y = 8.

Mathematics
1 answer:
Vika [28.1K]2 years ago
6 0

keeping in mind that perpendicular lines have negative reciprocal slopes, let's check for the slope of the equation above

-2x+4y=8\implies 4y=2x+8\implies y=\cfrac{2x+8}{4} \\\\\\ y=\cfrac{2x}{4}+\cfrac{8}{4}\implies y=\stackrel{\stackrel{m}{\downarrow }}{\cfrac{1}{2}}x+2\impliedby \begin{array}{|c|ll} \cline{1-1} slope-intercept~form\\ \cline{1-1} \\ y=\underset{y-intercept}{\stackrel{slope\qquad }{\stackrel{\downarrow }{m}x+\underset{\uparrow }{b}}} \\\\ \cline{1-1} \end{array}

since we know that's its slope, then

\stackrel{~\hspace{5em}\textit{perpendicular lines have \underline{negative reciprocal} slopes}~\hspace{5em}} {\stackrel{slope}{\cfrac{1}{2}} ~\hfill \stackrel{reciprocal}{\cfrac{2}{1}} ~\hfill \stackrel{negative~reciprocal}{-\cfrac{2}{1}\implies -2}}

so then we're really looking for the equation of a line whose slope is -2 and passes through (2 , 1)

(\stackrel{x_1}{2}~,~\stackrel{y_1}{1})\qquad \qquad \stackrel{slope}{m}\implies -2 \\\\\\ \begin{array}{|c|ll} \cline{1-1} \textit{point-slope form}\\ \cline{1-1} \\ y-y_1=m(x-x_1) \\\\ \cline{1-1} \end{array}\implies y-\stackrel{y_1}{1}=\stackrel{m}{-2}(x-\stackrel{x_1}{2}) \\\\\\ y-1=-2x-4\implies y=-2x-3

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The absolute value of x, denoted "| x |" (and which is read as "the absolute value of x"), is the distance of x from zero. This is why absolute value is never negative; absolute value only asks "how far?", not "in which direction?" This means not only that | 3 | = 3, because 3 is three units to the right of zero, but also that | –3 | = 3, because –3 is three units to the left of zero. You can see this on the following number line:

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As this illustrates, if you take the negative of an absolute value (that is, if you have a "minus" sign in front of the absolute-value bars), you will get a negative number for your answer.

Side note: When typing math as text, such as in an e-mail, the "pipe" character is usually used to indicate absolute values. The "pipe" is probably a shift-key somewhere north of the "Enter" key on your keyboard. While the "pipe" denoted on the physical keyboard key may look like a "broken" line, the typed character should display on your screen as a solid vertical bar. If you cannot locate a "pipe" character, you can use the "abs()" notation instead, so that "the absolute value of negative 3" would be typed as "abs(–3)".

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Simplify | 0(–4) |.

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