# Need help with finding exact values

#### sk8erboi

##### New member
Hey,

we're learning trig identities in school and finding exact values just makes no sense to me anymore. i was wondering if someone could help me - or at least point me in the right direction - with solving this:

Find the exact value of the following:

tan(7π/12)
sin105°

#### Subhotosh Khan

##### Super Moderator
Staff member
Hey,

we're learning trig identities in school and finding exact values just makes no sense to me anymore. i was wondering if someone could help me - or at least point me in the right direction - with solving this:

Find the exact value of the following:

tan(7π/12)
sin105°

Do you know the exact values of:

tan(π/4)

tan(π/3)

tan(A+B)

sin(45o)

sin(60o)

sin(A+B)

#### sk8erboi

##### New member
Do you know the exact values of:

tan(π/4)

tan(π/3)

tan(A+B)

sin(45o)

sin(60o)

sin(A+B)
yeah

tan(π/4) = 1

tan(π/3) = square root of 3

tan(A+B) = (tanA + tanB)/(1 - tanAtanB) .................Those parentheses are super important

sin(45o) = √2/2

sin(60o) = √3/2

sin(A+B) = sinAcosB + cosAsinB

What do i do from there though?

Last edited by a moderator:

#### Subhotosh Khan

##### Super Moderator
Staff member
yeah

tan(π/4) - 1

tan(π/3) - square root of 3

tan(A+B) - tanA + tanB/1 - tanAtanB

sin(45) - √2/2

sin(60º]) - √3/2

sin(A+B) - sinAcosB + cosAsinB

What do i do from there though?
Notice:

π/4 + π/3 = 7π/12

and

45º + 60º = 105º

What do you think you should do now?

#### sk8erboi

##### New member
Notice:

π/4 + π/3 = 7π/12

and

45o + 60o = 105o

What do you think you should do now?
OHH. I figured out the sin105 question, but the tan 7pi/12 question tripped me up. Now i feel stupid lmao thank you so much though

#### Jomo

##### Elite Member
Khan told you that π/4 + π/3 = 7π/12, you know the formula for tan(a+b) and you know the value of know tan(π/4) and tan (π/3)? So use this information in the formula for tan(a+b)