Answer:
C
Explanation:
If you notice, this is what the tangent-difference identity resembles. The tangent-difference identity is:
![\tan(\alpha-\beta)=(\tan(\alpha)-\tan(\beta))/(1-\tan(\alpha)\tan(\beta))](https://img.qammunity.org/2021/formulas/mathematics/college/9gsqsi40zw889zr9cszv9hymwz5v3ecyt0.png)
We have the expression:
![(\tan((\pi)/(7))-\tan((\pi)/(8)))/(1-\tan((\pi)/(7))\tan((\pi)/(8)))](https://img.qammunity.org/2021/formulas/mathematics/college/p57x5uo9qd42zo7wd7qyjkhl75zar6pl01.png)
So, our α is π/7 and our β is π/8. Therefore:
![(\tan((\pi)/(7))-\tan((\pi)/(8)))/(1-\tan((\pi)/(7))\tan((\pi)/(8)))=\tan((\pi)/(7)-(\pi)/(8)})](https://img.qammunity.org/2021/formulas/mathematics/college/qn8nnez12vxt5dq1mnd501c3v41sbwfpxd.png)
Simplify:
![(\tan((\pi)/(7))-\tan((\pi)/(8)))/(1-\tan((\pi)/(7))\tan((\pi)/(8)))=\tan((8\pi)/(56)-(7\pi)/(56)})](https://img.qammunity.org/2021/formulas/mathematics/college/q4t4cl7e5ox2bv3mjq462z0szl516b1yt5.png)
Subtract:
![(\tan((\pi)/(7))-\tan((\pi)/(8)))/(1-\tan((\pi)/(7))\tan((\pi)/(8)))=\tan((\pi)/(56))](https://img.qammunity.org/2021/formulas/mathematics/college/lxpsx907b6bx13oagt3i13pbq5bn6ca51d.png)
So, our answer is C.
And we're done!