Question Number 196166 by pticantor last updated on 19/Aug/23
$$\boldsymbol{{for}}\:\boldsymbol{{any}}\:\boldsymbol{{a}},\boldsymbol{{b}}\in\left[−\mathrm{1},\mathrm{1}\right]\:\:\boldsymbol{{calculate}}:\: \\ $$$$\boldsymbol{{arccos}}\left(\boldsymbol{{a}}\right)+\boldsymbol{{arcsin}}\left(\boldsymbol{{b}}\right)=? \\ $$$$\boldsymbol{{arcsin}}\left(\boldsymbol{{a}}\right)+\boldsymbol{{arcsin}}\left(\boldsymbol{{b}}\right)=? \\ $$$$\boldsymbol{{arccos}}\left(\boldsymbol{{a}}\right)+\boldsymbol{{arc}}{cos}\left(\boldsymbol{{b}}\right)=? \\ $$
Commented by pticantor last updated on 19/Aug/23
$${i}\:{make}\:{some}\:{unforgotable}\:{mistake}!\:{please}\: \\ $$
Answered by MM42 last updated on 19/Aug/23
$$\left.\mathrm{1}\right){cos}^{−\mathrm{1}} {a}={x}\Rightarrow{a}={cosx}\Rightarrow{sinx}=\sqrt{\mathrm{1}−{a}^{\mathrm{2}} } \\ $$$${sin}^{−\mathrm{1}} {b}={y}\Rightarrow{b}={siny}\Rightarrow{cosy}=\sqrt{\mathrm{1}−{b}^{\mathrm{2}} } \\ $$$${A}={x}+{y}\Rightarrow{sinA}={sinxcosy}+{sinycosx} \\ $$$$\Rightarrow{sinA}=\sqrt{\mathrm{1}−{a}^{\mathrm{2}} }\sqrt{\mathrm{1}−{b}^{\mathrm{2}} }+{ab} \\ $$$$\Rightarrow{A}={sin}^{−\mathrm{1}} \left(\sqrt{\left(\mathrm{1}−{a}^{\mathrm{2}} \right)\left(\mathrm{1}−{b}^{\mathrm{2}} \right)}+{ab}\right) \\ $$$$ \\ $$$$\left.\mathrm{2}\right){sin}^{−\mathrm{1}} {a}={x}\Rightarrow{a}={sinx}\Rightarrow{cosx}=\sqrt{\mathrm{1}−{a}^{\mathrm{2}} } \\ $$$${sin}^{−\mathrm{1}} {b}={y}\Rightarrow{b}={siny}\Rightarrow{cosx}=\sqrt{\mathrm{1}−{b}^{\mathrm{2}} } \\ $$$${A}={x}+{y}\Rightarrow{sinA}={sinxcosy}+{sinycosx} \\ $$$$\Rightarrow{sinA}={a}\sqrt{\mathrm{1}−{b}^{\mathrm{2}} }+{b}\sqrt{\mathrm{1}−{a}^{\mathrm{2}} } \\ $$$$\Rightarrow{A}={sin}^{−\mathrm{1}} \left({a}\sqrt{\mathrm{1}−{b}^{\mathrm{2}} }+{b}\sqrt{\mathrm{1}−{a}^{\mathrm{2}} }\right) \\ $$$$ \\ $$$$\left.\mathrm{3}\right){cos}^{−\mathrm{1}} {a}={x}\Rightarrow{a}={cosx}\Rightarrow{sinx}=\sqrt{\mathrm{1}−{a}^{\mathrm{2}} } \\ $$$${cos}^{−\mathrm{1}} {b}={y}\Rightarrow{b}={cosy}\Rightarrow{siny}=\sqrt{\mathrm{1}−{b}^{\mathrm{2}} } \\ $$$${A}={x}+{y}\Rightarrow{cosA}={cosxcosy}−{sinxsiny} \\ $$$${cosA}={ab}−\sqrt{\mathrm{1}−{a}^{\mathrm{2}} }\sqrt{\mathrm{1}−{b}^{\mathrm{2}} } \\ $$$$\Rightarrow{A}={cos}^{−\mathrm{1}} \left({ab}−\sqrt{\left(\mathrm{1}−{a}^{\mathrm{2}} \right)\left(\mathrm{1}−{b}^{\mathrm{2}} \right)\:}\right) \\ $$$$ \\ $$
Commented by pticantor last updated on 20/Aug/23
$${thank}\:{you}\:{too}\:{much}\:{sir} \\ $$