Final answer:
The value of f(x) at x=7 is 126. When decreased by three, the new value is 123.
Step-by-step explanation:
To calculate the value of the function f(x)=2x² +4x at x=7 and then decrease it by three, we first substitute x with 7:
f(7) = 2(7)² + 4(7)
= 2(49) + 28
= 98 + 28
= 126
After obtaining the value of f(x) for x=7, we decrease it by three:
f(7) - 3 = 126 - 3
= 123
Therefore, the decreased value of the function when x=7 is 123.