Simple harmonic motion question help

hi so I was doing the summary questions for 18.3 and stuck on question 2 ( as follows)

the displacement of an object oscillating in simple harmonic motion varies with time according to the equation x (mm) = 12cos10t where t = time in seconds after the object was at max positive displacement.

so for a (i) it said to calculate amplitude which I got as 12mm.
a (ii) was to find time period which I got as 0.6283185307 a
question (b) states what will by the displacement of the object when t = 0.1

I put t = 0.1 in the equation and got 11.99817234 mm

but the answer at the back says 6.5 mm what's going on? could someone please help me on where I went wrong? thank you!

hi so I was doing the summary questions for 18.3 and stuck on question 2 ( as follows)

the displacement of an object oscillating in simple harmonic motion varies with time according to the equation x (mm) = 12cos10t where t = time in seconds after the object was at max positive displacement.

so for a (i) it said to calculate amplitude which I got as 12mm.
a (ii) was to find time period which I got as 0.6283185307 a
question (b) states what will by the displacement of the object when t = 0.1

I put t = 0.1 in the equation and got 11.99817234 mm

but the answer at the back says 6.5 mm what's going on? could someone please help me on where I went wrong? thank you!

Convention is to work in radians for SHM rather than degrees - this would give 6.48... which rounds off to 6.5mm as required

6.5 is obtained using radians instead of degrees. In SHM radians are usually used, but I think in the actual exam they will probably specify.

cos10t is written in the form: $\text{cos}(\omega t)$

where $\omega = 2\pi f$

i.e. 360^o = $2\pi$ radians

hi so I was doing the summary questions for 18.3 and stuck on question 2 ( as follows)
the displacement of an object oscillating in simple harmonic motion varies with time according to the equation x (mm) = 12cos10t where t = time in seconds after the object was at max positive displacement.
so for a (i) it said to calculate amplitude which I got as 12mm.
a (ii) was to find time period which I got as 0.6283185307 a
question (b) states what will by the displacement of the object when t = 0.1
I put t = 0.1 in the equation and got 11.99817234 mm
but the answer at the back says 6.5 mm what's going on? could someone please help me on where I went wrong? thank you!