Limiting sum question (1 Viewer)

[miniwaybzz]

hey guys,
i dont really get the concept of ''limiting sum'' nor do i understand the textbooks explanation , anyways, can anyone help me with the HSC 04 paper Q9ii (i knew what to do in part i, just use the formula lol)

"for what values of in the interval does the limiting sum exist?"
ive got solutions and have no idea what they're on about :/

 

[_deloso]

hey guys,

"for what values of in the interval does the limiting sum exist?"
ive got solutions and have no idea what they're on about :/

for limiting sum to exist, the absolute value of the common ratio must be less than 1 (you need to know this). now the common ratio that we got from (i) is a trig function... therefore, we must solve for theta. and the theta value must be between -pi/2 and pi/2. if we solve for theta, we get that the answer is -pi/4<theta<pi/4 which is in between -pi/2 and pi/2

 

[_deloso]

we get that the answer is -pi/4 < theta < pi/4 which is in between -pi/2 and pi/2

 

[miniwaybzz]

ahhh okay i get it! thanks