the height h(t), in feet, of an airborn tee shirt t seconds after being launched can be approximated by h(t) = -15t^2 +45t +10, 0 is less than or equal to t less than or equal to 10. Find the times when the tee shirt will reach a fan 40' above ground level. The tee shirt will reach the fan at _____seconds.

Question

campbell_st · Answer

you need to let h(t) = 40 and solve for t

$$40 = -15t^2 + 45t + 10$$

or 

$$-15t^2 + 45t - 30 = 0$$

this can be factorised, here is the 1st part. 

$$-15(t^2 - 3t + 2) = 0$$

factorise the quadratic inside the brackets and you will find there are 2 solutions.  

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