Q. The function f is defined by f(x)=ax2+bx+c, where a,b, and c are constants and 1<a<4. The graph of y=f(x) in the xy-plane passes through points. (11,0) and (−2,0). If a is an integer, what could be the value of a+b ?
Set up equations: Since the graph of y=f(x) passes through the points (11,0) and (−2,0), we can set up two equations using these points to find the relationship between a, b, and c.f(11)=a(11)2+b(11)+c=0f(−2)=a(−2)2+b(−2)+c=0
Substitute x-values: Let's substitute the x-values from the points into the equations to get:a(11)2+b(11)+c=0a(−2)2+b(−2)+c=0
Simplify equations: Now we simplify the equations:121a+11b+c=04a−2b+c=0
Express c in terms: We have two equations with three unknowns, which means we cannot find the exact values of a, b, and c without additional information. However, we can express c in terms of a and b using one of the equations.Let's use the second equation to express c:c=−4a+2b
Substitute c into first equation: Substitute c from the fourth step into the first equation:121a+11b−4a+2b=0117a+13b=0
Find possible values of a: We need to find the values of a and b such that a is an integer and 1 < a < 4. Since a must be an integer, let's list the possible values of a: 2, 3.
Try a=2: First, let's try a=2 and solve for b using the equation 117a+13b=0: 117(2)+13b=0 234+13b=0 13b=−234 b=−234/13 b=−18
Try a=3: Now let's check if a=3 gives us an integer value for b: 117(3)+13b=0 351+13b=0 13b=−351 b=−351/13 b=−27
Calculate a+b: Both a=2 and a=3 give us integer values for b. Now we can calculate a+b for each case:For a=2, b=−18, so a+b=2−18=−16.For a=3, b=−27, so a=20.
Check valid values: Since the question asks for possible values of a+b, we have two possible answers: −16 and −24. However, we need to ensure that a+b is a single value, so we must check if both values of a are valid given the constraints of the problem.
Check valid values: Since the question asks for possible values of a+b, we have two possible answers: −16 and −24. However, we need to ensure that a+b is a single value, so we must check if both values of a are valid given the constraints of the problem.The constraints are 1 < a < 4 and a is an integer. Both a=2 and a=3 satisfy these constraints. Therefore, both −16 and −24 are valid answers for a+b.
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