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    d^2 = 25t^2 - 112t +169

    find the length of time to the nearest minute for which the distance is less than 11km
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    (Original post by examweek)
    d^2 = 25t^2 - 112t +169

    find the length of time to the nearest minute for which the distance is less than 11km
    d^2=121

    Form a quadratic and factorise .
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    (Original post by examweek)
    d^2 = 25t^2 - 112t +169

    find the length of time to the nearest minute for which the distance is less than 11km
     11^2 > 25t^2 -112t +169 \implies 0> 25t^2 -112t +48 \implies 25t^2 -112t +48 < 0

    Now find the critical values by solving,  25t^2 -112t +48 = 0

    At the end draw the graph, and find the required length of time.
 
 
 
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