What is the strongest part of your body? Your head? Bones? It's your teeth! There is a special thing called enamel (牙釉质) in teeth. It is the hardest thing in the human body and keeps bacteria (细菌) away. However, teeth are vulnerable (易受伤害的) to problems and disease. September 20 is National Teeth-loving Day in China. Let's pay attention to the health of our teeth.
    Tooth     (1)   are    (1)   around the world. Most children and young adults have tooth decay (龋齿). A study published on China Health Monthly magazine this year showed that 40.74 percent of a sample (抽样) of 1,306 Chinese students under age 15 had decayed teeth.
(2)Food that is rich in sugar increases the risk of tooth decay. After you eat, bacteria go crazy over the sugar on your teeth, like ants at a picnic. The bacteria turn sugar into acids (酸) that eat away at tooth enamel.This cause holes in your teeth.
    Another common problem is crooked teeth (龅牙). When your new teeth begin to grow and the old teeth haven't fallen out, there isn't enough space for the new ones. This causes crooked teeth.
    Don't worry. Here are some ways to keep your teeth healthy.
    Brush at least twice a day – in the morning and before bedtime.
    Learn to use dental floss (牙线). The floss gets rid of food that's hidden where your toothbrush can't get it.
    Visit a dentist. He or she can check if you have any dental problems and help you clean your teeth.
    Pay attention to what you eat. It is better to eat lots of fruits and vegetables instead of fries and drink water instead of soda.
    Wear braces (牙套) to make your teeth straight and beautiful.

小张同学利用打点计时器研究自由落体运动，他设计的实验方案如下：

如图甲所示，将打点计时器固定在铁架台上，先打开电源后释放重物，重物带动纸带从静止开始下落，打出几条纸带并选出一条比较理想的纸带如图乙所示，在纸带上取出若干计数点，其中每相邻计数点之间有四个点未画出，分别用s₁、s₂、s₃、s₄、s₅表示各计数点间的距离，已知打点计时器的频率f．图中相邻计数点间的时间间隔T=____（用f表示），计算重力加速度的公式是g=____（用f、s₂、s₅表示），计数点5的速度公式是v₅=____（用f、s₄、s₅表示）

已知sin(x+$\frac{\mathrm{\pi }}{6}$)=$\frac{1}{3}$，则sin(x-$\frac{5\mathrm{\pi }}{6}$)+sin²($\frac{\mathrm{\pi }}{3}$-x)的值是____