3. The first four terms of a sequence are: T2 = 12+ 22
T3 = 12 + 22 + 32
T4 = 12 + 22 + 32 +42
T1 = 12
The n" term is given by Tn=n(n + 1)(2n + 1).
Work out the value of T23.

The 23rd term is 2806.

Step-by-step explanation:

The other answerer has used the formula but i'm answering from the assumption that T1 to T4 are correct.

Each term is the sum of n terms of an arithmetic series with first term a1 = 12 and common difference d = 10.

Sum of n terms = (n/2)[2a1  + d(n - 1)]

So the sum of 23 terms =

= 23/2 (2*12 + 10 * 22)

= 11.5 * 244

= 2806.

answer

a,b, and d

explanation

a reflection angle is more than

but less than;

an angle that measures

is a reflex angle.(true)

an angle that measures less than

is acute.(true)

provided we are considering angles greater or equal to zero.

an acute angle lies in the range.

an obtuse angle is less than 180° but more than 90°

an angle that measures 300° is obtuse (false)

an angle that measures 65° is an acute angle.(true)