Помогите пожалуйста 499 (3,4) решить, я не могу

3) $\frac{(c-d)(c+d)-2c ^{2}}{c(c-d)} * \frac{-(c-d)}{c^{2} + d^{2} } = \frac{c ^{2} -d ^{2} -2c ^{2}}{c(c-d)} * \frac{-(c-d)}{c^{2} + d^{2} }=- \frac{-c ^{2}-d ^{2} }{c} * \frac{1}{c^{2} + d^{2} }=$ $\frac{c ^{2} +d ^{2} }{c} * \frac{1}{c^{2} + d^{2} }= \frac{1}{c}$
4) $\frac{2c ^{2} +(d-c)(d+c)}{c(c+d)}* \frac{c+d}{ c^{2}+ d^{2} } = \frac{2c ^{2} + d^{2}- c^{2} }{c(c ^{2} +d ^{2} )}= \frac{c ^{2} + d^{2} }{c(c ^{2} +d ^{2} )}= \frac{1}{c}$