If y varies directly with x, how do you find y when x = 3 if y = -3 when x =6?

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Answer 1 · 2017-05-17T08:59:06

#y = -3/2#

We can write direct variation in maths as:

#y prop x" "# Make an equation by using a constant (#k#)

#y = k xx x" "# Find the value of #k#

#y/x = k" "# Use the pair of values given #x=6 and y=-3#

#k =-3/6#

#k=-1/2" "# use this and the given #x# value to find #y#

#y = -1/2 xx 3#

#y = -3/2#

You can also write a direct proportion as equivalent fractions:

#x/y = (6)/-3 = 3/y" "# now cross multiply

#6y = -3 xx3#

#y = (-3xx3)/6#

#y = -9/6 = -3/2#