$$\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{tan}}{\left({\mathtt{a}}\right)} = {\frac{{\mathtt{7}}}{{\mathtt{24}}}}$$ $${\frac{\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{sin}}{\left({\mathtt{a}}\right)}}{\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{cos}}{\left({\mathtt{a}}\right)}}} = {\frac{{\mathtt{7}}}{{\mathtt{24}}}}$$ $$\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{sin}}{\left({\mathtt{a}}\right)} = {\frac{{\mathtt{7}}}{{\mathtt{24}}}}{\mathtt{\,\times\,}}\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{cos}}{\left({\mathtt{a}}\right)}$$ $${\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{sin}}{\left({\mathtt{a}}\right)}}^{\,{\mathtt{2}}}{\mathtt{\,\small\textbf+\,}}{\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{cos}}{\left({\mathtt{a}}\right)}}^{\,{\mathtt{2}}} = {\mathtt{1}}$$
substitute sin(a)=7/24*cos(a) into sin^2(a)+cos^2(a)=1
we have 49/576*cos^2(a)+cos^2(a)=1
625/576*cos^2(a)=1
cos^2(a)=576/625
since tan(a)>0 ,so we have,
In first quadrant , 0<a<pi/2 cos(a)=24/25 sin(a)=7/24*(24/25)=7/25
In third quadrant, pi<a<3pi/2 cos(a)=-24/25 sin(a)=7/24*(-24/25)=-7/25
given that cos(b)=-12/13 pi/2<b<3pi/2
when pi/2<b0 sin(b)=[1-(-12/13)^2]^(1/2)=5/13
when pi/2<b
$$\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{sin}}{\left({\mathtt{a}}{\mathtt{\,\small\textbf+\,}}{\mathtt{b}}\right)} = \underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{sin}}{\left({\mathtt{a}}\right)}{\mathtt{\,\times\,}}\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{cos}}{\left({\mathtt{b}}\right)}{\mathtt{\,\small\textbf+\,}}\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{cos}}{\left({\mathtt{a}}\right)}{\mathtt{\,\times\,}}\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{sin}}{\left({\mathtt{b}}\right)}$$
soloution 1 :when 0<a<pi/2 and pi/2<b<pi
sin(a+b)=7/25*(-12/13)+24/25*(5/13)=36/325
soloution 2 :when 0<a<pi/2 and pi<b<3/2*pi
sin(a+b)=7/25*(-12/13)+24/25*(-5/13)=-204/325
soloution 3:when pi<a<3pi/2 and pi/2<b<pi
sin(a+b)=-7/25*(-12/13)+(-24/25)*(5/13)=-36/325
soloution 4: when pi<a<3pi/2 and pi<b<3/2*pi
sin(a+b)=-7/25*(-12/13)+(-24/25)*(-5/13)=204/325
(edited)
$$\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{tan}}{\left({\mathtt{a}}\right)} = {\frac{{\mathtt{7}}}{{\mathtt{24}}}}$$ $${\frac{\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{sin}}{\left({\mathtt{a}}\right)}}{\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{cos}}{\left({\mathtt{a}}\right)}}} = {\frac{{\mathtt{7}}}{{\mathtt{24}}}}$$ $$\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{sin}}{\left({\mathtt{a}}\right)} = {\frac{{\mathtt{7}}}{{\mathtt{24}}}}{\mathtt{\,\times\,}}\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{cos}}{\left({\mathtt{a}}\right)}$$ $${\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{sin}}{\left({\mathtt{a}}\right)}}^{\,{\mathtt{2}}}{\mathtt{\,\small\textbf+\,}}{\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{cos}}{\left({\mathtt{a}}\right)}}^{\,{\mathtt{2}}} = {\mathtt{1}}$$
substitute sin(a)=7/24*cos(a) into sin^2(a)+cos^2(a)=1
we have 49/576*cos^2(a)+cos^2(a)=1
625/576*cos^2(a)=1
cos^2(a)=576/625
since tan(a)>0 ,so we have,
In first quadrant , 0<a<pi/2 cos(a)=24/25 sin(a)=7/24*(24/25)=7/25
In third quadrant, pi<a<3pi/2 cos(a)=-24/25 sin(a)=7/24*(-24/25)=-7/25
given that cos(b)=-12/13 pi/2<b<3pi/2
when pi/2<b0 sin(b)=[1-(-12/13)^2]^(1/2)=5/13
when pi/2<b
$$\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{sin}}{\left({\mathtt{a}}{\mathtt{\,\small\textbf+\,}}{\mathtt{b}}\right)} = \underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{sin}}{\left({\mathtt{a}}\right)}{\mathtt{\,\times\,}}\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{cos}}{\left({\mathtt{b}}\right)}{\mathtt{\,\small\textbf+\,}}\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{cos}}{\left({\mathtt{a}}\right)}{\mathtt{\,\times\,}}\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{sin}}{\left({\mathtt{b}}\right)}$$
soloution 1 :when 0<a<pi/2 and pi/2<b<pi
sin(a+b)=7/25*(-12/13)+24/25*(5/13)=36/325
soloution 2 :when 0<a<pi/2 and pi<b<3/2*pi
sin(a+b)=7/25*(-12/13)+24/25*(-5/13)=-204/325
soloution 3:when pi<a<3pi/2 and pi/2<b<pi
sin(a+b)=-7/25*(-12/13)+(-24/25)*(5/13)=-36/325
soloution 4: when pi<a<3pi/2 and pi<b<3/2*pi
sin(a+b)=-7/25*(-12/13)+(-24/25)*(-5/13)=204/325
(edited)