Multiple Choice

Suppose [tex]y[/tex] varies directly with [tex]x[/tex], and [tex]y = 14[/tex] when [tex]x = -4[/tex]. What is the value of [tex]y[/tex] when [tex]x = -6[/tex]?

A. [tex]-21[/tex]
B. 10
C. 18
D. 21



Answer :

To solve the problem where [tex]\( y \)[/tex] varies directly with [tex]\( x \)[/tex], we need to use the concept of direct variation, which means [tex]\( y = kx \)[/tex] for some constant [tex]\( k \)[/tex].

1. Determine the constant [tex]\( k \)[/tex]:
- We are given that [tex]\( y = 14 \)[/tex] when [tex]\( x = -4 \)[/tex].
- Substitute these values into the equation to find [tex]\( k \)[/tex]:
[tex]\[ 14 = k \times (-4) \][/tex]
- Solve for [tex]\( k \)[/tex]:
[tex]\[ k = \frac{14}{-4} = -3.5 \][/tex]

2. Use the constant [tex]\( k \)[/tex] to find the new value of [tex]\( y \)[/tex] when [tex]\( x = -6 \)[/tex]:
- Substitute [tex]\( k \)[/tex] and the new [tex]\( x \)[/tex] value into the direct variation equation:
[tex]\[ y = k \times (-6) \][/tex]
- Substitute [tex]\( k = -3.5 \)[/tex]:
[tex]\[ y = -3.5 \times (-6) = 21 \][/tex]

Thus, the value of [tex]\( y \)[/tex] when [tex]\( x = -6 \)[/tex] is [tex]\( 21 \)[/tex].

Therefore, the correct answer is
[tex]\[ \boxed{21} \][/tex]